1. Field of the Invention
The present invention relates to a switch and, more particularly, to a snap-action switch for use where the operation thereof is accomplished by a slowly moving activation device, such as a timing mechanism.
2. Discussion of the Prior Art
There are many applications wherein it is desirable to control the operation of a switch using a slowly moving timing mechanism. For example, interval timing devices for coin operated appliances, such as laundry machines, employ timing mechanisms which operate to activate a snap-action switch through a gear arrangement.
Unfortunately, snap-action switches have an inherent disadvantage with respect to the manner in which they are constructed when used in such application. Basically, a snap-action switch is a spring loaded toggle arm which, when moved a predetermined distance, will snap from a first position to a second position. Because the arm is spring loaded, its contact portion remains in abutment with a first stationary contact until displacement of the switch button causes the arm to move a predetermined distance to cause its contact portion to snap to the second position. However, when the button is pressed very slowly, there is a short period of time whereby the moving arm contact is no longer tightly pressed against or in pressing abutment with the first stationary contact and has not snapped over to the secondary contact. This is referred to as the deadband zone of the switch, that is, the switch is hung-up in the sense that it is in an unstable state between its first and second positions.
Typically, the activating button of the switch can be pushed slowly for between 1/1000th and 3/1000ths of an inch after pressed abutment with the first stationary contact has been broken and before the snapping action occurs. If the switch is used in a timing arrangement, and the switch contact controls the time as well as the coin operated appliance, this means that with the movement of the switch contacts apart from each other, the timing motor will stop, often before the switch has snapped to its second position. With the contacts suspended a small fraction of an inch from each other, any vibration--either physical or thermal--will cause the contacts to close briefly and perhaps spring open again in a flutter. When the contacts are pressing slightly against each other, in the sense that they are barely touching, a high resistance path for the flow of electric current is established. Current flowing through this path will generate heat which may be sufficient to destroy or burn out the contacts, or cause them to weld together. Fluttering the power source to electric motors and/or overheating of the motors, including the appliance motor and the timing motor, can cause damage to the appliance and possible injury to an unwary operator. This can also overheat the contacts to cause premature failure of the switch itself. In fact, it is not uncommon for switch manufacturers to refuse to guarantee snap-action switches when used in a timing arrangement or other slow activating arrangement.
It is therefore an object of the invention to provide a means whereby the effect of the deadband zone on the operation of the snap-action switch is substantially eliminated.